For forming an integral body in which a copper-base material is received within the bore of a tubular iron-base material, one of the following prior art techniques is generally used.
(1) Casting: A molten copper-base material is cast into the bore of an iron-base material.
(2) Diffusion joining: A copper-pipe material is first inserted or forced into the bore of an iron-base material. Then, these materials are heated and diffusion-joined by utilizing the difference between their coefficients of thermal expansion and the transformative contraction of iron.
(3) Brazing: A copper-base pipe material is first inserted into the bore of an iron-base material. Then, a brazing filler metal is heated and applied in the gap between the iron-base material and the copper-base pipe material so that the filler metal penetrates into the gap to establish a bond between the iron-base material and the copper-base pipe material.
These prior art methods, however, suffer from their inherent problems. The first method (1) has the problems that: (i) the use of large amounts of flux in order to achieve improved bonding ability harms the working environment; and (ii) excess copper-base material needs to be cast, which leads to poor yield, considerable amounts of processing in the post treatment subsequent to casting, and consequently, high cost.
The following problems have been encountered by the second and third methods (2), (3). (i) Unless the diameter and surface roughness of the bore of the iron-base material and the outside diameter and surface roughness of the copper-base pipe material are adjusted with high precision, bonding rate will vary to a considerable extent and the percentage of defective products will increase. Supervision for ensuring such absolute precision incurs additional cost. (ii) Materials that can be used for forming the copper-base pipe material are limited and the production of the copper-base pipe material is expensive.
Another known technique is sinter-joining in which a tubular copper-base material is forced into the bore of a tubular iron-base material and the materials are wholly heated and joined to each other to produce an integral body. In this method, a means such as a jig is used for pressurizing the copper-base material in its expanding direction from inside in order to prevent defective joining due to the shrinkage of the copper-base material. However, it is difficult to ensure high bonding quality with this method because of the difficulty in uniform pressure transmission.
The invention has been made for the purpose of overcoming the foregoing problems and one of the objects of the invention is therefore to provide a sinter-joining method capable of achieving high bonding quality in joining a copper-base material to an iron-base material by sintering without incurring additional cost. Another object of the invention is to provide a sintered composite member produced by this method.